The present invention relates to a crystallized tetramethylbiphenyl type epoxy resin which is easy to blend with a hardener or the like, a method for producing the crystallized epoxy resin, and a curable epoxy resin composition excellent in various properties comprising the crystallized epoxy resin.
Epoxy resins are used in wide fields such as adhesion, casting, encapsulation, lamination, molding and coating because of their excellent curing and easy-handling properties.
In general, epoxy resins are used by being mixed (blended) with various additives, including a hardener, being molded into a curable epoxy resin composition, and being cured. However, if each component is not uniformly mixed upon blending, such phenomena may occur that a curing reaction does not proceed sufficiently, and that a cured product becomes heterogeneous, and its performance cannot sufficiently be attained.
Because tetramethylbiphenyl type epoxy resins obtained by the reaction of 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetramethylbiphenyl with an epihalohydrin are crystals having a melting point of from 100xc2x0 C. to 120xc2x0 C., they are widely used in applications, such as powder coating and semiconductor encapsulation, wherein they are solids at ordinary temperature and melted by raising the temperature to fluidize upon molding and/or curing. However, since they are crystals, there are such defects that their compatibilization with a hardener or the like is slow and poor mixing tends to occur. If the temperature upon blending is higher than the melting point, so as to uniformly mix, the reaction with a hardener proceeds at that time and poor fluidization tends to occur upon molding. Further, if a mixing time is prolonged, productivity decreases, which is industrially disadvantageous.
The present invention relates to a crystallized tetramethylbiphenyl type epoxy resin which is easy to blend with a hardener or the like, a method for producing the crystallized epoxy resin, and a curable epoxy resin composition excellent in various properties comprising the crystallized epoxy resin.
As a result of various investigations to solve the above-mentioned problems, the present inventors have found that a crystal of tetramethylbiphenyl type epoxy resin having a specific melting endothermic pattern quickly compatibilizes with a hardener or the like, whereby a uniform curable epoxy resin composition is easily obtained, and that a certain crystallized tetramethylbiphenyl type epoxy resin quickly compatibilizing can be obtained under specific crystallizing conditions, and have completed the present invention.
The present invention includes each of the following inventions.
(1) A crystallized epoxy resin, which is a crystallized product of an epoxy resin derived from 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetramethylbiphenyl and an epihalohydrin, wherein the ratio of an endotherm (the amount of heat absorbed) between 50xc2x0 C. and 130xc2x0 C. to an endotherm between 80xc2x0 C. and 125xc2x0 C., measured by raising the temperature at a rate of 10xc2x0 C. per minute using a DSC device, is 1.03 or more.
(2) The crystallized epoxy resin as described in (1), wherein the ratio of an endotherm between 50xc2x0 C. and 130xc2x0 C. to an endotherm between 80xc2x0 C. and 125xc2x0 C., measured by raising the temperature at a rate of 10xc2x0 C. per minute using a DSC device, is between 1.05 and 1.50, and the endothermic peak temperature is 110xc2x0 C. or lower.
(3) A method for producing a crystallized epoxy resin having a ratio of an endotherm between 50xc2x0 C. and 130xc2x0 C. to an endotherm between 80xc2x0 C. and 125xc2x0 C. of 1.03 or more, measured by raising the temperature at a rate of 10xc2x0 C. per minute using a DSC device, comprising cooling an epoxy resin derived from 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetramethyl-biphenyl and an epihalohydrin and having an epoxy equivalent of 180 to 210, from the molten state at 105xc2x0 C. or higher, and nearly completely crystallizing within 2 hours after the temperature reaches lower than 105xc2x0 C.
(4) The method for producing a crystallized epoxy resin as described in (3), wherein the ratio of an endotherm between 50xc2x0 C. and 130xc2x0 C. to an endotherm between 80xc2x0 C. and 125xc2x0 C., measured by raising the temperature at a rate of 10xc2x0 C. per minute using a DSC device, is between 1.05 and 1.50, and the endothermic peak temperature is 110xc2x0 C. or lower.
(5) The method for producing a crystallized epoxy resin as described in (3) or (4), wherein the step of cooling from the molten state at 105xc2x0 C. or higher and nearly completely crystallizing the epoxy resin within 2 hours after the temperature reaches lower than 105xc2x0 C., comprises adding a crystal nucleus and/or applying a shear force.
(6) A curable epoxy resin composition comprising a blend of a crystallized epoxy resin derived from 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetramethylbiphenyl and an epihalohydrin and having a ratio of an endotherm between 50xe2x80x2 C. and 130xc2x0 C. to an endotherm between 80xc2x0 C. and 125xc2x0 C. of 1.03 or more, measured by raising the temperature at a rate of 10xc2x0 C. per minute using a DSC device, and a hardener for epoxy resins, as essential components.
(7) The curable epoxy resin composition as described in (6), wherein the crystallized epoxy resin has a ratio of an endotherm between 50xc2x0 C. and 130xc2x0 C. to an endotherm between 80xc2x0 C. and 125xc2x0 C., measured by raising the temperature at a rate of 10xc2x0 C. per minute using a DSC device, of between 1.05 and 1.50, and an endothermic peak temperature of 110xc2x0 C. or lower.